Trying to package kdelibs for the Guix distribution, which currently does not contain udev, the following problem occurs.

Udev is of course not found:
...
-- checking for module 'libudev'
--   package 'libudev' not found
-- Could NOT find UDev (missing:  UDEV_INCLUDE_DIR UDEV_LIBS)
-- Building Solid HAL backend.
-- Building Solid UPower backend.
-- Building Solid UDisks2 backend.
-- Building Solid fstab backend.
...
-- The following OPTIONAL packages have not been found:
...
 * UDev , UDev support for Solid , <http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev.html>
   Allows Solid to use UDev to provide information about devices on Linux
...

Nevertheless, the build later fails:
Linking CXX shared library ../../lib/libsolid.so
cd /tmp/nix-build-kdelibs-4.13.0.drv-0/build/solid/solid && /gnu/store/rzfbvn6nkdcccgrcphl8hyqwcjqddhr5-cmake-2.8.12/bin/cmake -E cmake_link_script CMakeFiles/solid.dir/link.txt --verbose=1
/gnu/store/6z7k9ms4sf367c3phl7djhb740ly3dqi-gcc-4.8.2/bin/c++ -fPIC ...
CMakeFiles/solid.dir/backends/udisks2/udisksopticaldisc.o: In function `Solid::Backends::UDisks2::OpticalDisc::~OpticalDisc()':
/tmp/nix-build-kdelibs-4.13.0.drv-0/kdelibs-4.13.0/solid/solid/backends/udisks2/udisksopticaldisc.cpp:344: undefined reference to `UdevQt::Device::~Device()'
(and further undefined references of this kind).


Reproducible: Always

Steps to Reproduce:
1. Compile kdelibs on a machine without udev, I suppose.
2.
3.